Most of the combustion processes used in industry use air as an oxidizer to combust a fuel such as natural gas, fuel oil, propane, waste oils, other hydrocarbons and the like. Performance of many air-fuel combustion processes can be improved by enriching the combustion air with oxygen. Enrichment of the combustion air increases both the flame temperature and the thermal efficiency while the flue gas volume decreases as the oxygen concentration in the oxidizer increases. Increased costs due to the use of high purity oxygen for enrichment can be offset by gains in productivity from enhanced combustion. Low level enrichment of up to 35% total oxygen content in the oxidizer can generally be applied to existing air-fuel systems with only a few modifications to the system.
Low level oxygen enrichment in combustion can cause dramatic increases in NOX emissions. Under the U.S. Clean Air Act, there are regulations, if not incentives, for controlling the NOX formations as a result of combusting air-fuel mixtures in the presence of oxygen. Most industrial combustion processes producing NOX emissions result in over 90% of the NOX emissions being in the form of nitric oxide or NO. It is known that high levels of oxygen enrichment, e.g. above 90% total oxygen content in the oxidizer, produce less NOX than using air at the same firing rate. However, high levels of oxygen enrichment can be uneconomical for a given process and in fact may lead to problems with equipment.
U.S. Pat. No. 5,308,239 discloses and claims a method for reducing NOX production during air-fuel combustion processes utilizing oxygen enrichment.
U.S. Pat. No. 5,217,363 discloses and claims a method and apparatus for using air-oxygen techniques for combustion of hydrocarbon fuels wherein the air is primarily used to cool the burner during firing.
U.S. Pat. No. 4,797,087 discloses and claims a method and apparatus for using air-oxygen techniques for combustion of hydrocarbon fuels.